1. Field of the Invention
The present invention relates to an electronic camera capable of performing stroboscope imaging and a white balance correction circuit applied to the electronic camera.
2. Description of the Related Art
In general, white balance correction values of an electronic camera are determined according to the color temperature of illumination that illuminates a subject and to the type of the illumination. The color temperature and type of the illumination can be obtained, for example, from an image of the subject and from an output of a colorimeter. The white balance correction values are determined by not only the color temperature of the illumination but also the type of the illumination because two different types of illumination (e.g., illumination of fluorescent light and that of natural light) having the same color temperature may have significantly different color renderings.
On the other hand, at stroboscope imaging a subject is illuminated with double illumination of strobe light and field light (light other than the strobe light). Therefore, it is preferable that the white balance correction values should be decided according to the type and color temperature of the field light as well as the type and color temperature of the strobe light. However, the type and color temperature of the strobe light is actually unique to the stroboscope device. At present the following methods (1) through (4) are proposed for determining the white balance correction values at stroboscope imaging.
(1) A method in which the white balance correction values are so determined as to suppress the color of the single illumination of the strobe light on the assumption that strobe light provides a much stronger influence on the subject than any field light.
(2) A method in which the type and color temperature of the field light are obtained from a pre-imaging prior to strobe light emission or an output of a colorimeter to average such values that suppress the color of the single illumination of the field light and such values that suppress that of the strobe light, thereby determining the average values as the white balance correction values.
(3) A method in which, further to the method (2), the intensity of the field light is measured to estimate an amount of the strobe light emission (i.e., the degree of influence which the strobe light has on the subject), and the foregoing averaging is weighted in accordance with the degree of influence.
(4) A method in which the type and color temperature of the field light are determined from a pre-imaging prior to a strobe light emission or from an output of a colorimeter, and then a subject distance is measured to estimate how much amount of the strobe light reaches the subject, thereby selecting either values that suppress the color of the single illumination of the field light or values that suppress that of the strobe light in accordance with the estimated amount (and further, the measurement of the subject distance, the estimation of the reaching light amount, and the value selection are performed for every area of the field.)
According to the method (1), however, the white balance correction is made by use of the same white balance correction values so that a certain stroboscopic image will be extremely inappropriately reproduced. For example, in a case where strobe light does not sufficiently reach the background of a subject because of a long distance, and besides the color temperature of the illumination to the background is low, an image captured in this condition may have unnaturally reddish background.
According to the methods (2), (3) and (4), they may be adaptable to a variety of stroboscopic images but reproduced images by these methods cannot gain users' satisfaction in spite of the fact that they are complex processing.